1. Field of the Invention
This invention relates to the use of electroreduction for the elimination of nitrate esters and nitro compounds from industrial process waste water streams. This invention relates particularly to a process for the treatment of industrial process waste water containing dissolved nitrate esters and nitro compounds as contaminants.
2. Description of the Prior Art
At the present time there is no economically acceptable process for the treatment of industrial process waste waters containing dissolved nitrate esters and nitro compounds. These pollutants represent a serious threat to our water resources if not adequately removed from process waste water before it is disposed of in our streams, rivers and lakes. In the manufacture of nitroglycerin and other nitrate esters, it has been necessary to wash the crude nitration product to remove dissolved acids. It is then necessary to wash the nitroglycerin with sodium carbonate solutions to neutralize the remaining acid and stabilize the product against autocatalytic acid decomposition. It has been standard practice to discharge these wash waters containing dissolved nitroglycerin into streams to prevent the localized buildup of nitroglycerin in the ground. Other methods that have been used or proposed for the treatment of waste waters containing explosive wastes include distillation of the waste water over sodium hydroxide or other strong caustic substances, aspiration of the waste water into a flame, reduction with sulfides, and activated carbon adsorption. Both distillation and aspiration into a flame are economically unattractive due to the high energy consumed. Chemical treatments, such as reduction with sulfides, create additional pollutants, including some reaction products more toxic than nitroglycerin, which then require further treatment.
Prior art relating to the electroreduction process of this invention includes a general discussion of electroreduction found in the Encyclopedia of Chemical Technology, Volume 5, Interscience, New York, 1950, pages 495 and 662-667. In addition, a paper by F. Kaufman, H. J. Cook and S. M. Davis, J. Am. Chem. Soc. 74, 4997 (1952), describes the polarography of nitrate esters, specifically, ethyl and cyclohexyl nitrate. Also, it is well known in the art to use an electrolytic reduction process as a synthesis tool, where yield is of primary importance for reduction of nitro compounds as disclosed in U.S. Pat. Nos. 700,670 to Buchner, 700,672 to Buchner, 736,204 to Buchner, 736,205 to Buchner, 761,984 to Buchner, and 1,926,837 to Cupery. In the processes disclosed in the prior art, solutions are concentrated and conditions are carefully controlled to maximize yield and limit side reactions. For example, a diaphragm is often placed between electrodes to prevent undesired subsequent reactions. None of these references disclose treatment of industrial process waste water streams containing dissolved nitrate esters and nitro compounds. In addition, none of these references is concerned with elimination of nitrate esters and nitro compounds as pollutants in water.